The work of specifying the Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) consisting of the Long Term Evolution (LTE) and System Architecture Evolution (SAE) concepts is currently ongoing within the 3rd Generation Partnership Project (3GPP). The architecture of the LTE system is shown in FIG. 1.
The E-UTRAN consists of base stations called enhanced NodeBs (eNBs or eNodeBs), providing the E-UTRA user plane and control plane protocol terminations towards the User Equipment (UE). The eNBs are interconnected with each other by means of the X2 interface. The eNBs are also connected by means of the S1 interface to the EPC (Evolved Packet Core), more specifically to the MME (Mobility Management Entity) by means of the S1-MME interface and to the Serving Gateway (S-GW) by means of the S1-U interface. The S1 interface supports many-to-many relation between MMEs/S-GWs and eNBs.
The eNB hosts functionalities such as Radio Resource Management (RRM), radio bearer control, admission control, header compression of user plane data towards serving gateway, routing of user plane data towards the serving gateway. The MME is the control node that processes the signaling between the UE and the core network (CN). The main functions of the MME are related to connection management and bearer management, which are handled via Non Access Stratum (NAS) protocols. The S-GW is the anchor point for UE mobility, and also includes other functionalities such as temporary downlink (DL) data buffering while the UE is being paged, packet routing and forwarding the right eNB, gathering of information for charging and lawful interception. The packet data network (PDN) Gateway (P-GW) is the node responsible for UE IP address allocation, as well as Quality of Service (QoS) enforcement (this is explained further below). FIG. 2 gives a summary of the functionalities of the different nodes, and 3GPP TS 36.300 is referred to and the references therein show the details of the functionalities of the different nodes. FIG. 2 shows logical nodes, functional entities of the control plane and radio protocol layers.
Using Wireless Fidelity/Wireless Local Area Network (WiFi/WLAN) (the two terms are used interchangeably throughout this document) to offload traffic from the mobile networks is becoming more and more interesting from both the operators' and end users' points of view.
The Access Network Discovery and Selection Function (ANDSF) is an entity defined by 3GPP for providing access discovery information as well as mobility and routing policies to the UE. ANDSF is a new entity added to the 3GPP architecture in Release 8 of 3GPP TS 23.402. By supplying information about available both 3GPP and non-3GPP access networks to the UE, the ANDSF enables an energy-efficient mechanism of network discovery, where the UE can avoid continuous and energy-consuming background scanning. Furthermore, the ANDSF provides the mobile operators with a tool for the implementation of flexible and efficient UE steering of access mechanisms, where policy control can guide UEs to select one particular radio access network (RAN) over another.
It is currently being discussed in 3GPP whether to introduce a parameter signaled from the 3GPP RAN to be used in an ANDSF policy. One example of such a parameter is called “Offloading Preference Indicator (OPI)”.